The specific objectives of this project are as follows: 1. To determine those sequences of events wic characterize the onset of respiration in the newborn lamb, with regard in particular to lung fluid clearance (net filtration pressures across the pulmonary vascular bed, changesin pulmonary lymph flow, capillary permeability, and net lung fluid volume), and changes in pulmonary retractive properties (tracheal effluent lecithin concentrations; sequential changes in pulmonary compliance and airway conductance; pulmonary extract surface tension studies); and 2. To determine the alterations in these various parameters which may occur as a consequence of prenatal asphyxia. As a corollary to our interest in the effects of intrauterine "stress" on neonatal pulmonary characteristics, we are also investigating the effects of prenatal hydrocortisone administration on the pulmonary mechanical properties of the newborn lamb and rehesus monkey.